It comes in a small teal box with a label that says "New Boomerang Pet Ball. Really Works!" The ball is a boomerang, hence the name. It can be thrown and returns to whoever threw it.
Role in the episode
When SpongeBob attempts to get Gary to take a bath, he throws the ball towards the bathtub. However, the ball bounces back. Later, SpongeBob throws the box but it bounced back at his head when he was beginning to walk away.